Observations of meteor-head echoes using the Jicamarca 50MHz radar in interferometer mode
[摘要] We present results of recent observations of meteor-head echoes obtained with the high-power large-aperture Jicamarca 50MHz radar(11.95°S, 76.87°W) in an interferometric mode.The large power-aperture of the system allows us to record morethan 3000 meteors per hour in the small volume subtended by the1° antenna beam, albeit when the cluttering equatorialelectrojet (EEJ) echoes are not present or are very weak.Theinterferometry arrangement allows the determination of the radiant(trajectory) and speed of each meteor. It is found that theradiant distribution of all detected meteors is concentrated inrelative small angles centered around the Earth's Apex as ittransits over the Jicamarca sky, i.e. around the correspondingEarth heading for the particular observational day and time, forall seasons observed so far.The dispersion around the Apex is~18° in a direction transverse to the Ecliptic planeand only 8.5° in heliocentric longitude in the Eclipticplane both in the Earth inertial frame of reference. Noappreciable interannual variability has been observed. Moreover,no population related to the optical (larger meteors) Leonidshowers of 1998-2002 is found, in agreement with other largepower-aperture radar observations.
A novel cross-correlation detection technique (adaptivematch-filtering) is used in combination with a 13 baud Barkerphase-code. The technique allows us to get good range resolution(0.75km) without any sensitivity deterioration for the sameaverage power, compared to the non-coded long pulse scheme used atother radars. The matching Doppler shift provides an estimation ofthe velocity within a pulse with the same accuracy as if anon-coded pulse of the same length had been used. The velocitydistribution of the meteors is relatively narrow and centeredaround 60kms-1. Therefore most of the meteors have analmost circular retrograde orbit around the Sun. Less than 8% ofthe velocities correspond to interstellar orbits, i.e. withvelocities larger than the solar escape velocity(72kms-1). Other statistical distributions of interestare also presented.
